This invention relates to instant reusable cold and hot compresses, and more particularly to reusable compresses capable of initially producing cold or heat by thermochemical reaction.
Instant compresses have long been used to apply cold or heat to human or animal body parts. Previous known compresses contain materials such as inorganic salts which chill or heat a fluid within the compress. The fluid used has generally been water or water mixed with chemicals possessing a high thermal capacity such as propylene glycol. The primary drawback of this technology is that these prior art instant compresses are not reusable. Also, the compresses eventually leak causing a loss of the internal fluid. Compresses which use high heat capacity chemicals such as propylene glycol have the added problem that the leaking fluid is toxic.
There are orthopedic devices in the prior art which are used to treat injured body parts by immobilizing the body part and applying cold or heat compresses. For example U.S. Pat. No. 4,964,402 discloses an orthopedic device for treatment of injured joints or limbs having at least one gel pad containing at least one phase change material for improving thermal energy storage capacity. The phase change material is pre-distributed throughout the gel matrix. Externally generated cold or heat is applied to the gel pad. The phase change material is selected so that it will undergo a phase change while the cold gel is reheating or the hot gel is cooling. In this manner, the U.S. Pat. No. 4,964,402 invention uses the latent heat of fusion of the phase change material to improve the heat capacity of the gel material. While the gel pad may be reused in the orthopedic device there is no means to provide an instant cooling or heating effect due to the method of dispersal of the phase change material. The orthopedic devices themselves are specialized to fit and immobilize specific body parts.
Inorganic salt hydrates combined with synthetic polymers to form a thermochemical energy storage material have been previously described. U.S. Pat. No. 4,574,051 describes the use of a hydrated salt suspended in synthetic polymers like polyvinyl alcohol, polyacrylic acid, polyethylene oxide and acrylamide polymers. In the U.S. Pat. No. 4,574,051 thermal storage device, only the latent heat of fusion of the salt hydrate is utilized. The patented device involved a material with an improved heat capacity. The inorganic salt would be pre-suspended in the synthetic polymer matrix hence ruling out any ability to create instant cold or heat effects.
The same is true for the thermal storage materials described in U.S. Pat. Nos. 4,273,667 and 4,545,916. In the U.S. Pat. No. 4,273,667, the thermal storage material is comprised of at least one hydrated compound, such as an inorganic salt, having a reversible transition to the anhydrous or less hydrated form and a hydrogel. The hydrogel was comprised of a water swollen cross linked polymer throughout which the hydrated compound was dispersed. Some of the polymers described in the U.S. Pat. No. 4,273,667 include a copolymer of acrylic acid with acrylamide. Calcium chloride was mentioned as a possible hydrated compound. Only the use of the salt heat of fusion was described in the U.S. Pat. No. 4,273,667 as the hydrated compound is pre-dispersed in the polymer matrix. U.S. Pat. No. 4,545,916 described a heat storage material in which sodium pyrophosphate decahydrate is dispersed throughout an open cell polymeric matrix. One of the polymeric matrices mentioned is formed by crosslinking a water soluble polymer having pendant carboxylic acid groups by means of cations of polyvalent metal or by a covalent crosslinking mechanism. The purpose of the phosphate salt is to improve the heat capacity of the polymer through the use of the salts heat of fusion. As the salt is pre-dispersed in the polymer matrix, the heat of the solution is not utilized.
There are many manufacturers of instant cold and hot compresses in North America and Europe. Their compresses are made with various types of flexible plastic containers which require them to be sealed on two or more sides. The process of sealing plastic is not an exact science resulting in containers which have a propensity to leak during or after activation. In the case of cold compresses this causes the patient to be put at risk of being subject to a frost bite burn from the escaping liquid which is at a temperature possibly as low as 15 degrees Fahrenheit. In the case of hot compresses, the patient may be exposed to a toxic liquid substance and the activated liquid which may have a temperature as high as 185 degrees Fahrenheit.
Prior art instant cold and hot compresses are made to be discarded after one use. If a patient tries to reuse a prior art compress by boiling the compress, placing it in a microwave oven, or placing it in a freezer, the compress bag-like container will usually break down because it is not made of a durable plastic material which will stand up to repeated use. Also, in the case of cold compresses, the compress when placed in a freezer will become hard and not have the ability to conform to the patient's body. Furthermore, should the compress leak the corrosive nature of the product may oxidize the metal finish of the inside of the freezer compartment.
Where attempts have been made to combine instant thermal reactions with a reusability feature, they have been limited. For example, U.S. Pat. No. 4,462,224 to Dunshee et al. discloses a three compartment, instant hot or cold, reusable cold pack for transferring heat to or from an object. A first compartment contains a solvent comprised primarily of water. A second compartment contains a particulate solute which is capable of dissolving in the first compartment solvent whereby a predetermined amount of heat is liberated or absorbed. The third compartment contains a gelling agent capable of gelling with the solvent and solute solution at ambient temperature. Mixing the contents of the first compartment and the second compartment provides an instant heating or cooling effect as in an instant hot or cold pack. Once the solution has returned to ambient temperature, the contents of the third compartment can be mixed with the contents of the first and second compartments to produce a gel. U.S. Pat. No. 4,967,573 to Wilhelm simplifies the Dunshee et al. pack with a two compartment construction. However, the gelling agent used is deliberately selected so that the agent will not actually form a gel until the cooling takes place and after the cold produced in the instant pack mode leaves the pack through normal use.